Daylight readable liquid crystal display

ABSTRACT

A daylight readable LCD which may be used to communicate information as high contrast images (static or dynamic, color or monochrome) in bright ambient lighting conditions over a wide temperature range in direct sunlight. A contrast enhancement filter assembly is disposed at the interface between a backlit display and a user. The contrast enhancement filter assembly includes a triple bandpass contrast enhancement filter that preferably passes light efficiently in each of the red, green, and blue primary wavelengths and substantially absorbs all other wavelengths. Display contrast is increased because of the absorption of incident light having wavelengths that differ from the light produced by the internal backlight source within the display. This results in the display having a blacker background and enhanced purity of the color primaries. The display element is disposed generally behind the contrast enhancement filter assembly. An air gap separation is preferably provided between the contrast enhancement filter assembly and the display element to allow a heat conducting medium to flow therebetween to control thermal loading of the display. A fluorescent backlight assembly provides at least about 5,000 fL of illumination. An air gap separation is preferably provided between the display element and the backlight to allow a heat conducting medium to flow therebetween to control thermal loading of the display. The ratio of output light to reflected incident ambient light is at least about 5:1.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 08/901,683,filed Jul. 28, 1997 for “Daylight Readable Liquid Crystal Display,” nowU.S. Pat. No. 5,754,262, which is a continuation of application Ser. No.08/421,371, filed Apr. 11, 1995 for “Daylight Readable Liquid CrystalDisplay,” abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a display device for displaying images, andmore particularly to a liquid crystal display device for generating anddisplaying images having sufficient contrast to be easily seen in brightdaylight.

2. Description of the Related Art

A persistent problem in the art of electronically generating anddisplaying images is generating an image with sufficient contrastbetween light and dark areas to permit the features of the image to beeasily discerned in bright sunlight and over a wide temperature range.The principal reason that many display technologies, including liquidcrystal displays (LCDs) and cathode ray tubes (CRTs), are difficult toread in bright ambient light conditions is that they reflect asignificant amount of incident ambient light, which essentially masksany emissive or transmissive light from the display. For example, thephosphors on CRTs reflect about 70% to 80% of incident light. Thephosphor luminance forming displayed information simply gets overcome bythe reflected luminance, rendering the display illegible in directsunlight. Similarly, active matrix LCD (AMLCD) panels reflect about 50%of incident light. overcome by the reflected luminance, rendering thedisplay illegible in direct sunlight. Similarly, active matrix LCD(AMLCD) panels reflect about 50% of incident light.

Sunlight is accepted in industry to be 10,000 foot candles of incidentillumination with a spectral energy distribution profile that favors theblue wavelengths of light. It is also accepted in industry that contrastvalues of 5:1 or higher are necessary in high ambient lightingconditions if the display is to be daylight readable. This means anemissive display with high background reflectance, such as a CRT, wouldneed to emit on the order of 35,000 fL-40,000 fL to be legible in directsunlight. Considering that CRT displays that produce 200 fL-300 fL ofluminance at their face are considered exceptional, achieving such ahigh level luminance in an emissive panel is extremely difficult.

In addition to such problems with emissive displays, it would bedesirable for a number of reasons, such as power consumption and displaysize, to be able to use LCDs (sometimes referred to as light valvedisplays) as outdoor displays. Possible uses would be bank ATM machinesand information kiosks. However, to date, such displays have not beendaylight readable.

A typical LCD assembly consists of a liquid crystal cell and two linearpolarizers. A first linear polarizer is disposed on the front surface ofthe liquid crystal cell. A second linear polarizer is disposed on theback of the liquid crystal cell. The polarizer can be envisioned as afine parallel line grating having parallel lines spaced equidistantapart. For the linear polarizer to provide the effect needed for an LCD,the width of the lines and spaces of the polarizer must be approximatelythe size of the wavelength of light the polarizer is intended toselectively pass. The E-vector of light provided by a typical lightsource used with an LCD is generally completely random in orientation.However, only incident light waves having E-vectors aligned with thegrating of the polarizer pass through virtually unaltered. The dark bodyof the polarizer in a liquid crystal display absorbs light that does nothave aligned E-vectors, whether that light is incident on the front ofthe LCD or source from the rear. A good quality linear polarizer willpass 40$ to 45% of randomly aligned incident light (50% is thetheoretical limit for linear polarizers).

The light valve resident between the polarizers is the liquid crystalcell. Liquid crystal materials are typically long chain-like moleculesthat have the unique property of being able to rotate from a first axisto a second axis of orientation when a voltage is applied across thecell gap. The degree of rotation is principally controlled by themagnitude of the voltage across the cell. The cell, in reference to thepolarizers, can be thought of as a shutter. When the cell is turned on,it allows light from the rear illumination source (backlight) to passcompletely through the assembly. When the cell is turned off, thedisplay is dark. For color LCD displays, color filters are placed overdiscrete cell locations in a pixel pattern or mosaic) one each red,green, and blue sub-pixel making a white color dot) and the emissionspectra in the backlight is matched to the color filters to make a colordisplay.

LCD transmissive displays have inherently higher contrast in highambient lighting environments than emissive displays because of thedark, nearly black, background color of the linear polarizer. The darkbody of the polarizer in a liquid crystal display absorbs most light,whether incident on the front or sourced from the rear, that does nothave a specific E-vector. However, some background reflectance ofambient light still occurs, particularly with Almonds. To meet the 5:1contrast discussed earlier and overcome the effects of the backgroundreflectance on the front surface due to sunlight, the LCD assembly wouldneed to provide about 1,000 fL of luminance at its front face. Whilethis is a lot less than emissive displays, it is still a very brightdisplay (i.e., backlight) and beyond practical limitations imposed onsuch systems, such as the amount of heat which may be generated in avery high power system. For reference, typical notebook computerdisplays produce 20 fL-40 fL at the face of the display. State of theart military LCD displays generate as much as 200 fL at the displayface.

Another problem with using conventional LCD panels in direct sunlight isdue to heat. Typically, the majority of light incident on an LCD panelis absorbed. Light energy absorbed in the polarizer is translated intoheat. Light absorption is a desirable optical characteristic, but suchabsorption increases the temperature of the liquid crystal cell, andthus limits the useful ambient temperature range of the displays. Liquidcrystal displays can only perform optimally over a narrow band oftemperatures (typical about 0° C. to 40° C.). At temperatures below 0°C., the liquid crystal material loses its mobility and cannot readilyreact to a voltage applied across the cell gap. At temperatures above40° C., referred to as the “clearing temperature”, a condition known as“clearing” occurs in which all cells move to an open state. Accordingly,information content is lost because there is no discernible contrast inthe display.

The clearing temperature of a light crystal cell can be reached in atleast two ways. First, the ambient air temperature can directly raisethe temperature of the liquid crystal material. Second, the temperatureof the liquid crystal material can be elevated by external thermalloading, such as from direct sunlight, even if the ambient temperatureis below the clearing temperature for the material. External thermalloading from direct sunlight is more particularly known as solarloading. Accordingly, because an LCD can clear due to solar loading evenwhen the ambient air temperature is well below the clearing temperature,solar loading imposes limitations on where and how LCDs can be used.

Therefore, there is currently a need for an LCD which is easily readablein daylight and which is usable over a wide temperature range in directsunlight.

SUMMARY OF THE INVENTION

The present invention is a daylight readable color LCD which may be usedto communicate information as high contrast images (static or dynamic,color or monochrome) in bright ambient lighting conditions over a widetemperature range in direct sunlight.

The present invention preferably has three major components. The firstmajor component is a contrast enhancement filter assembly that isdisposed at the interface between the display and the user. The contrastenhancement filter assembly includes a triple bandpass contrastenhancement filter that preferably passes light at three selectedwavelengths, and absorbs essentially all other visible light. Thecontrast enhancement filter assembly preferably passes light efficientlyin each of the red, green, and blue primary wavelengths necessary tomake white light in an additive color system. Display contrast isincreased by use of the contrast enhancement filter because of theabsorption of incident light having wavelengths that differ from thelight produced by the internal backlight source within the display. Thisresults in the display having a blacker background and enhanced purityof the color primaries. In the preferred embodiment, an anti-reflectioncoating is provided on the two dominant surfaces of the contrastenhancement filter.

The second major component of the preferred embodiment of the presentinvention is the display element. The display element is disposedgenerally behind the contrast enhancement filter assembly. An air gapseparation is preferably provided between the contrast enhancementfilter assembly and the display element to allow a heat conductingmedium to flow therebetween. In the present context, the term “heatconducting medium” is used to generically refer to a gas, liquid orother heat conductor that is capable of either cooling or heating thedisplay element to maintain the liquid crystal material in the liquidcrystal cell within an optimum operating temperature range.

The display element is preferably a passive matrix LCD (PMLCD), althoughthe invention may be used with a properly treated active matrix LCD(AMLCD). In the preferred embodiment, the exposed surface of the frontpolarizer is provided with an antireflection coating.

The third major component of the preferred embodiment of the presentinvention is a backlight assembly. The backlight assembly is any sourceof randomly oriented light and preferably is capable of generating atleast 5,000 fL. In one embodiment, the backlight assembly is afluorescent dimmable backlight.

A physical separation is preferably provided between the backlight andthe display element. The physical separation preferably permits a heatconducting medium to remove heat from the back surface of the displayelement. This reduces the affects of thermal loading from the backlightassembly. In an alternative embodiment of the present invention, theheat conducting medium may be a solid which fills the separation. Thesolid acts as a heat source or heat sink to provide temperaturestabilization to the liquid crystal material.

The details of the preferred embodiment of the present invention are setforth in the accompanying drawings and the description below. Once thedetails of the invention are known, numerous additional innovations andchanges will become obvious to one skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of one embodiment of the present inventionshowing the three major components comprising the inventive display.

FIG. 2 a is a graph of the relative spectral transmittance of thecontrast enhancement filter used in the preferred embodiment.

FIG. 2 b is a graph of the relative spectral radiance of a display usingthe contrast enhancement filter of the preferred embodiment.

FIG. 3 is a 1976 CIE u′, v′ chromaticity diagram.

Like reference numbers and designations in the various drawings refer tolike elements.

DETAILED DESCRIPTION OF THE INVENTION

Throughout this description, the preferred embodiment and examples shownshould be considered as exemplars, rather than as limitations on thepresent invention.

The present invention is a daylight readable LCD display which may beused to communicate information as images in bright ambient lightingconditions and over a wide temperature range.

There are at least two ways in which the contrast of a transmissive LCDdisplay can be enhanced. Firstly, a significantly greater luminance canbe provided in the backlight to make a brighter display. Secondly, theamount of reflected ambient light can be reduced. The present inventionoptimizes the use of both techniques.

FIG. 1 is an illustration of one embodiment of the present invention inwhich three major components comprise the inventive display 100. Thefirst of the three major components is a backlight assembly 102including a light source. The second major component is a displayelement 103, preferably a passive matrix LCD panel. The third majorcomponent is a contrast enhancement assembly 105.

The backlight assembly 102 preferably is a very high intensity lightsource, preferably having at least 5,000 fl of luminance. In thepreferred embodiment, the backlight assembly 102 is the backlightdescribed in U.S. patent application Ser. No. 08/150,355, assigned tothe assignee of the present invention. However, any conventional lightsource having sufficient brightness and similar emissive spectra may beused, such as a conventional fluorescent light fixture, a conventionalincandescent light fixture, a halogen light fixture, or any other lightsource.

The preferred backlight assembly 102 comprises a fluorescent cavity 104coated with phosphors that are activated by a phosphor illuminator 106.In accordance with the preferred embodiment of the present invention,the phosphor illuminator 106 comprises an ultraviolet (UV) gas dischargelamp (not shown) having no coating of phosphor, internally orexternally, in or on the tube. The light tube is preferably fabricatedto provide the highest UV flux density per unit volume of the internalplasma.

The phosphors within the fluorescent cavity 106 used in the preferredbacklight assembly 102 of a color display 100 are selected so the peakemission spectra of each is predominantly at approximately 600-660 nm(red), 500-560 nm (green), or 400-460 nm (blue). The red, green, andblue phosphors are blended to produce an aggregate white output, thespectral characteristics of which can be “tuned” by varying theproportions of the blend.

The phosphors are the primary source of light in the backlight However,in the preferred embodiment, mercury is used in the lamp as the sourceof UV in the gas discharge lamp, as disclosed in the above referencedpatent application. A benefit of mercury is two strong emissions at 546nm green and 436 nm blue. The 546 emission line of the mercury isrelatively close to the 545 emission line of the green phosphor.Therefore, the 546 emission line provides the appearance of a slightlybroader emission band in the green light region. The 436 emission lineof mercury gives the appearance of a phosphor peak. Therefore, the 436emission line of the mercury provides greater amplitude to the phosphoremission from the 447 nm blue phosphors. Accordingly, both mercuryemission lines are used similarly to the phosphor and add to theluminance of the display.

In a passive matrix LCD, transmittance through the LC material,polarizers, color filters, and deposited metal for row and column tracesis typically about 2.5% to 5%. Due to the absorption and reflections oflight by the display element 103, a passive matrix LCD panel equippedwith the preferred high intensity backlight can provide about 200-300 fLat its front surface. A typical PMLCD will reflect about 4% to 8% of thelight incident on the polarizer. Therefore, this value is still muchless than the 1,000 fL required for a daylight readable display which isnot in accordance with the present invention. Since it is not at presentpractical to manufacture significantly more luminance in the backlightto make a brighter display, the only way to achieve greater contrast isto reduce the reflections of ambient or background light.

Light (illustrated by arrows 108 in FIG. 1) that is emitted from thebacklight assembly 102 passes through a first physical separation or airgap 110 and strikes the back surface of the display element 103. Theseparation 110 minimizes direct conduction of heat from the backlightassembly 102 to the display element 103. The separation 110 also allowsa heat conducting medium, such as air, to flow between the backlightassembly 102 and the display element 103. In the present context andthroughout this description, the term “heat conducting medium” is usedto generically refer to a gas, liquid, or solid heat conductor capableof conducting heat either from or to the display element. Accordingly,the heat conducting medium is capable of either cooling or heating thedisplay element 103 to maintain the liquid crystal material in theliquid crystal cell within an optimum operating temperature range. Forexample, in an alternative embodiment, a solid heat conductor may becoupled to a heat sink or source to maintain the temperature of thedisplay element 103 within a desired temperature range. In the preferredembodiment, the heat conducting medium is air which flows through theseparation due to convection currents. The air flowing over the surfaceof the display element 103 reduces the affects of thermal loading on theliquid crystal display 103 from the backlight assembly 102. In thepreferred embodiment, the separation 110 is about 1 mm to about 5 mm.

In the preferred embodiment, the display element 103 has linearpolarizers 112, 120 affixed to the back surface 116 and front surface118, respectively, of a liquid crystal cell 114. The liquid crystal cell114 is preferably activated by a conventional LCD drive circuit (notshown). The orientation of the first and second polarizers 112, 120 andthe configuration of the first and second polarizer 116, 120 and theliquid crystal cell 114 are conventional. In the preferred embodiment ofthe present invention, the second polarizer 120 has an anti-reflectioncoating 122 applied to the exposed front surface 124. The antireflectioncoating 122 is conventional and helps to prevent light that originatesfrom sources outside the display 100 from reflecting back to a viewer126. For example, the anti-reflection coating 122 may be vacuumdeposited magnesium fluoride, zirconium oxide, or other metallic oxide.

In the preferred embodiment, when a passive matrix LCD is used as thedisplay element 103, all of the reflective surfaces (such as the metalthat make up the row and column traces) are treated in known fashion tominimize reflections.

Light (illustrated by arrows 132 in FIG. 1) that is transmitted throughthe display element 103 passes through a second physical separation orair gap 128 and strikes the rear surface 134 of the contrast enhancementassembly 105. The separation 128 prevents direct conduction of heat fromthe contrast enhancement assembly 105 to the display element 103 andvice-versa. The separation 128 also allows a heat conducting medium,such as air, to flow between the contrast enhancement assembly 105 andthe display element 103. In the preferred embodiment, the separation 128is about 1 mm to about 5 mm.

In accordance with the preferred embodiment of the present invention,the contrast enhancement assembly 105 comprises a contrast enhancementfilter 130 with each of the dominant surfaces 134, 135 having aconventional anti-reflection coating 136 applied thereto. The contrastenhancement filter 130 is preferably an absorptive “triple-pass”homogenous composition filter (such as glass type S-8807, distributed bySchott Corporation of Duryea, Pa.) which passes light primarily in eachof the three primary color (RGB) regions and absorbs most other light.FIG. 2 a is a graph of the relative spectral transmittance of the filterused in the preferred embodiment. FIG. 2 b is a graph of the relativespectral radiance of a display equipped with such a contrast filter. Thecontrast enhancement filter 130 absorbs a portion of ultraviolet,visible, and near infra-red light energy that strikes the filter 130.Absorption by the contrast enhancement filter 130 of the portion of thetotal solar spectrum reduces solar loading (heat loading) of the liquidcrystal cell 114. Because the filter 130 is not physically attached tothe display element 103, direct coupling of the heat to the liquidcrystal cell 114 is inhibited.

Also, as the name implies, the contrast enhancement filter 130 enhancesthe contrast of the image generated by the display element 103. Thisenhancement is due to the additional absorption, especially atwavelengths that are not produced by the backlight assembly 102 (i.e.,light at wavelengths other than the wavelengths of light intentionallyproduced by the phosphors within the fluorescent cavity 104). In thepreferred embodiment, the contrast enhancement filter 130 absorbs atleast about 70% of incident light having wavelengths centered aroundabout 540 nm and about 580 nm (i.e., between blue and green, and greenand red, respectively). Conversely, in the preferred embodiment, thecontrast enhancement filter 130 passes at least about 70% of incidentlight having wavelengths centered around about 447 nm (blue), 545 nm(green), and 626 nm (red).

It should be noted that incident sunlight must pass through the contrastenhancement filter 130 in two directions (i.e., first entering and thenexiting) before becoming background light which might obscure theintended display image if the incident light was not absorbed by thecontrast enhancement filter 130 or otherwise blocked. Thus, sunlight atwavelengths outside the primary pass bands of the contrast enhancementfilter 130 is reduced by an additional 3 dB.

For example, sunlight that strikes the front surface of the display 100first encounters the front surface anti-reflection coating 136. As isknown, such anti-reflection coatings reduce surface specular(mirror-like) reflections. Accordingly, no more than about 2%, andpreferably only about 0.3%, of incident (first surface) light isreflected. The light which is neither absorbed nor reflected by theanti-reflection coating 136 passes through contrast enhancement filter130 for a first time. The contrast enhancement filter 130 absorbs asubstantial portion (at least about 30%) of the total incident lightresponsible for thermal loading (i.e., wavelengths in the range of100-1200 nm). In the preferred embodiment, the contrast enhancementfilter 130 absorbs about 100% of UV radiation (100-380 nm), at leastabout 20% of the total visible spectrum (380-780 nm), and at least about20% of near-infrared radiation (780-1200 nm).

The light that is not absorbed by the contrast enhancement filter 130passes through the rear surface anti-reflection coating 136, whichreduces light reflections from the rear surface, and between thecontrast enhancement filter and the display element 103.

Thereafter, the remaining ambient light that has passed through thecontrast enhancement assembly 105 enters the display element 103, wheremuch of such light is absorbed by the front polarizer 118. A portion(about 2%) of this light is reflected by the metal traces and otherfeatures of the liquid crystal cell 114. A relatively small amount oflight is also reflected by other elements of the display element 103,such as filter dyes and laminate materials used in construction of theLCD. All of the reflected light must then pass through the contrastenhancement assembly 105 once again. Therefore, any portion of the lightthat is at wavelengths other than the color primaries will again besubstantially absorbed. In fact, even those components of the reflectedlight that are in the primary regions will be attenuated (however, to amuch lesser degree than non-primary region light), since the contrastenhancement filter 130 is not perfectly transparent, even in the primaryregions.

Use of a triple-pass filter also enhances the color purity of thedisplay, because the filter absorbs strongly between the primaryemitters. Accordingly, any secondary and tertiary emissions resident inthe backlight are “filtered” from the observer 126. This results in anenhancement in the purity of the color primary that is visiblysignificant (there are fewer satellite emissions in close proximity tothe principal emitter that would otherwise desaturate the desiredcolor). When the color primaries are more saturated, the total potentialcolor palette increases, as illustrated on the 1976 CIE u′, v′chromaticity diagram (FIG. 3). The total number of potential colors isdefined as all the colors contained within the boundaries of thetriangle constructed from straight lines drawn between the green/red301, red/blue 302, and blue/green 303 chromaticity points.

Because of the light energy absorbed by the contrast enhancement filter130, the contrast enhancement assembly 105 is heated. As noted above,the separation 128 provided between the display element 103 and thecontrast enhancement filter assembly 105 helps reduce the affects ofthermal loading on the liquid crystal display 103 from the contrastenhancement filter assembly 105.

The structure illustrated in FIG. 1 and described above provides twosubstantial advantages over the prior art. First, the spacings orseparations 128, 110 between the major components 102, 103, 105 of thedisplay 100 allow a heat conducting medium to conduct heat to or fromeach component 102, 103, 105 and thus reduce any affects of thermalloading that would otherwise cause the temperature of the liquid crystalmaterial within the liquid crystal cell 114 to rise in temperature, andthus reduce the effective temperature range of the display 100. Second,the use of a triple-pass contrast enhancement filter 130 at theinterface between the user and the display provides a very substantialdecrease in background light. Furthermore, the use of anti-reflectioncoatings on each disjunctive surface reduces the amount of reflectance,and thus the background light.

Accordingly, the present invention provides a substantial increase inthe contrast of the image generated. That is, the contrast ratio oftransmitted light to reflected light is at least about 5:1 in room lightexceeding about 5,000 foot candles of incident illumination. Inexperiments using the preferred embodiments described above, thecontrast ratio exceeds about 20:1 under similar conditions.

A color PMLCD working model of the invention has been built inaccordance with the above described preferred embodiment. The prototypehas an operating temperature in the range of about 0° C. to about 40° C.The prototype display has a image area with a diagonal dimension ofapproximately 9.4 inches, and consumes approximately 75 W. (Of course,alternative embodiments may be larger or smaller, and use more or lesspower). In bright sunlight of about 10,000 foot candles of incidentillumination, the prototype display absorbs at least about 50% of theincident external light, reflects less than about 0.3% of the incidentlight, and has a ratio of transmitted light to reflected incident lightof about 10:1, well in excess of the 5:1 ratio generally deemed to berequired for daylight readability.

A number of embodiments of the present invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, the present invention may use a monochromatic contrastenhancement filter 130 with a monochrome LCD panel when the display isto generate monochromatic images. Furthermore, while the presentapplication focuses on the use of a passive matrix LCD, the inventionmay be used with an active matrix LCD. Also, any orientation of thepolarizers with respect to the liquid crystal display may be used inaccordance with the present invention. Still further, a wide variety ofgases, liquids, or solids may be used as the heat conducting medium inthe separations between the components of the inventive display.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiment, but only by the scope ofthe appended claims.

What is claimed is:
 1. A daylight readable display for use in brightambient light comprising: (a) a backlight source for providing initialtransmitted light; (b) a display element adjacent the backlight sourcefor modulating the initial transmitted light to display images; and (c)a selective-pass front filter in front of the display element, havingthe characteristics: (1) absorbing heat energy in a solar radiantspectrum of incident ambient light; (2) transmitting the modulatedinitial transmitted light from the display element; and (3) selectivelyfiltering incident ambient light; wherein the combination of backlightsource, display element, and filter reduce heating of the displayelement and provide a ratio of output light to reflected incidentambient light of at least about 5:1.
 2. The display of claim 1 whereinthe selective-pass filter absorbs 20% or more of incident ambient lightresponsible for thermal solar loading.
 3. The display of claim 2 whereinat least one surface of the display element has an anti-reflectivecoating.
 4. The display of claim 1 wherein the selective-pass filter isa triple-pass filter.
 5. The display of claim 1 wherein theselective-pass filter passes about 70% or more of incident light atgenerally blue, green, and red wavelengths.
 6. The display of claim 1wherein the selective-pass filter absorbs at least about 70% of theincident light having wavelengths generally between blue and green lightand between green and red light.
 7. The display of claim 1 wherein theselective-pass filter reflects less than 2% of incident ambient light.8. The display of claim 1, wherein the display element includes: (a) afirst polarizer for polarizing light; (b) a liquid crystal cell adjacentthe first polarizer for selectively altering the orientation of theE-field of incident light polarized by the first polarizer; and (c) asecond polarizer adjacent the liquid crystal cell for polarizing lightaltered by the liquid crystal cell.
 9. The display of claim 1 wherein atleast two surfaces of the display element have an anti-reflectivecoating.
 10. The display of claim 1 wherein at least one surface of theselective-pass filter has an anti-reflective coating.
 11. The display ofclaim 1 wherein the selective-pass filter absorbs about 30% of theincident ambient light responsible for thermal loading.
 12. The displayof claim 1 wherein the selective-pass filter absorbs at least 50% of theincident ambient light.
 13. The display of claim 1 wherein theselective-pass filter reflects less than about 0.3% of incident ambientlight.
 14. The display of claim 1 wherein the ratio of output light toreflected incident ambient light is at least 10:1.
 15. The display ofclaim 1 wherein the ratio of output light to reflected incident ambientlight is at least about 20:1.